mitcho (Michael Yoshitaka Erlewine) on "can hookpress trigger a custom wordpress post action?"

For your first question, unfortunately no. HookPress helps an external service know when a WordPress event occurs, but not the other way around, which is what I believe you would like to do.

Some of the others may be possible. Please take a look at the set of filters and actions exposed by WordPress which HookPress can use:

http://codex.wordpress.org/Plugin_API/Filter_Reference
http://codex.wordpress.org/Plugin_API/Action_Reference